From EP 1 910 670 BI a wind power plant is known comprising a generator for generating electrical energy, a rotor driving the generator with pitch-adjustable rotor blades and a central control device, wherein individual pitch devices are provided for the rotor blades, comprising an adjusting drive unit, a communication link to the central control device and a regulator, wherein the rotor blades can be brought into a stop position in order to shut down the wind power plant. The individual pitch devices each also comprise a fault detector and their own triggering mechanism, wherein the fault detector is configured to recognise abnormal operating states and is connected to the triggering mechanism, which causes the respective rotor blade to be moved into an off position.
A conventional safety system is shown in FIG. 6, wherein an EFC signal, which is triggered by a higher-order controller and/or directly by various emergency stop/sensor devices, is carried from a controller (e.g. topbox) on a single channel via a transmission device (e.g. slip ring) to a pitch system. The EFC signal is as a rule a 24V DC signal, wherein the expression EFC is an abbreviation of the term “Emergency Feather Command”. In the pitch system, this signal is distributed across the three drive systems. If this EFC signal is triggered, e.g. due to a signal state change, for all three drive systems a travel to the safe position (end position) is initiated. The EFC signal thus represents a control command to the safety switching device, to rotate the rotor blades to the safe position or end position.
If an error occurs in this EFC safety chain, e.g. due to induction of interference voltage, the initiation of a travel to the safe position via this EFC signal is no longer possible. At the same time however, the control system (turbine control) also recognises the faults and initiates corresponding measures via the communication system (bus system). Thus, the turbine control and the bus system are a component part of a SRP/CS and must comply with the requirements of the Machinery Directive. The expression SRP/CS used here is an abbreviation of Safety-Related Parts of Control System.
The above procedure in the event of a fault is associated with drawbacks, however, of which some are indicated below:
the bus system and control system (turbine control) are a component part of a SRP/CS and must be considered in the light of the Machinery Directive;
there is no longer any distinction between control system and safety system;
errors in the transmission device (e.g. slip ring) can cause faults in the bus system and/or in the EFC signal.